Many products today require highly engineered elastic components and yet, at the same time, must be produced at a cost consistent with limited use or disposability. By limited use or disposable, it is meant that the product and/or component is used only a small number of times or possibly only once before being discarded. Examples of such products include, but are not limited to, personal care absorbent products such as diapers, training pants, incontinence garments, and so forth. These products can and do utilize as components, elastic films, elastic fabrics, elastic filaments and/or elastic laminates.
Production of elastomeric filaments, elastic films, elastic nonwovens and elastic laminates has been accompanied by persistent problems of buildup of the composition being extruded on the die tip causing machine downtime for cleanup, frequently after only a few hours of operation. Various mechanisms are known to facilitate the cleaning and maintenance of dies used for the extrusion of polymer materials, while minimizing downtime. Molten polymers are extruded through dies to form films, strands, nonwoven webs, and other finished polymer forms. Particularly with elastic polymer compositions containing elastomers, as polymer exits the die, some of the polymer composition clings to the die openings or “lips,” accumulating on the exterior surface of the die. Die lip build-up gradually increases until it accumulates to a point where it breaks off, possibly causing a defect in the product, which can be, for example, in the form of thin spots or tears or otherwise deleterious effects on the texture or other esthetic properties of the product as well as other defects that are the result of stoppage. Considerable engineering goes into the design of dies and selection of extrusion compositions to minimize this build-up. Diverging, converging, radiused, and angled die lip geometries all are examples of methods developed to minimize this build-up. However, no die design completely eliminates it. It is common practice to temporarily halt the extrusion operation to perform maintenance on the die to remove this build-up. Stoppages adversely affect production yields, increase costs and may also adversely affect product uniformity. Accordingly, it is advantageous to minimize work stoppages.
Methods of reducing die lip build up or accumulation of extrudate contamination during extrusion have been attempted. For example, U.S. Pat. No. 6,245,271 describes a method of reducing die lip build up during extrusion that utilize a die having die lips with a radius of curvature of from about 0.5 mils to about 3 mils. It would be advantageous to develop a method for reducing die lip build up during extrusion. Particularly, it would also be advantageous to develop a method of reducing die lip build up during extrusion of elastomeric compositions that does not require modification of existing equipment.
Additionally, commercial processes commonly make multiple products at ranges of filament basis weights on the same die thus creating a need for a broad process window for manufacturing. For example, a 9 gram per square meter (gsm) filament sheet can be extruded at a specific throughput from a die. In order to increase the filament weight, a higher throughput is needed in the same die. The increase in throughput creates an increase in the shear rates and can create flow instabilities at the die exit. This phenomenon is commonly seen with melt fracture or shark skinning on the surface of an extruded filament. It would also be advantageous to increase the throughput range of a process without investing in multiple dies.